diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644
index 0000000..5dc69ff
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,64 @@
+# Contributing to any2bazel
+
+Contributions are welcome. This document explains how to contribute and which
+checks must pass before a change can merge.
+
+## EngFlow CLA
+
+All contributions require a signed EngFlow Contributor License Agreement (CLA)
+on file before they can be merged. If you have not signed one, a maintainer
+will let you know how to do so when you send your first change.
+
+## Discuss major changes first
+
+For anything larger than a small fix, please reach out and discuss the change
+with the maintainers before investing significant effort. Open an issue at
+https://github.com/EngFlow/any2bazel describing the problem and your proposed
+approach. This avoids duplicated work and changes that don't fit the project's
+direction.
+
+## Changes must be complete
+
+Each change should be a complete solution:
+
+* Changes to `scripts/` must include tests in `tests/`.
+* Changes to a script's arguments, output, or behavior must update `SKILL.md`
+  and any affected documentation in the same change.
+* Bug fixes should include a test that fails without the fix.
+
+Keep changes focused, smaller changes ensure faster reviews.
+
+## Code style
+Python code in this project generally follows [PEP
+8](https://peps.python.org/pep-0008/). When in doubt, follow the style of the
+surrounding code.
+
+## Sending changes
+
+Send changes as pull requests to https://github.com/EngFlow/any2bazel. Make
+sure all presubmit requirements below pass.
+
+## Presubmit requirements
+
+### Python tests
+
+CI runs the test suite with pytest in a fresh virtual environment. To
+reproduce locally:
+
+```bash
+python -m venv .venv
+.venv/bin/pip install pytest
+.venv/bin/pytest tests/
+```
+
+### Copyright headers
+
+All source files must begin with the Apache 2.0 license header.
+
+```bash
+bazel run //infra/internal/check_copyright_headers
+```
+
+> [!IMPORTANT]
+> The check inspects files in `HEAD`, not the working tree. **Commit your
+> changes before running it**, or new files will not be checked.
diff --git a/README.md b/README.md
index ef26786..ba8636b 100644
--- a/README.md
+++ b/README.md
@@ -74,8 +74,9 @@ deterministic diff drives the loop — an LLM does only the creative work
 
 ## Contributing
 
-Contributions are welcome. Please send any feedback and changes to the main
-repo at https://github.com/EngFlow/any2bazel.
+Contributions are welcome. See [CONTRIBUTING.md](CONTRIBUTING.md) for
+contribution flows and requirements. Please send any feedback and changes to the
+main repo at https://github.com/EngFlow/any2bazel.
 
 [license]: https://img.shields.io/badge/license-Apache%202.0-blue.svg
 [license-url]: LICENSE
diff --git a/SKILL.md b/SKILL.md
index fa05f5e..9dd1fdd 100644
--- a/SKILL.md
+++ b/SKILL.md
@@ -186,10 +186,10 @@ flags. Tests are opt-in (`include_tests`) and get the compile-parity stage only
 
 ## Procedure
 
-> **Script paths vs. project paths.** The `scripts/…` and `tests/…` paths below
-> are relative to **this skill's own directory** (where this `SKILL.md` lives) —
-> NOT the project being migrated. When running inside a target repo, invoke them
-> by absolute path, e.g.
+> **Script paths vs. project paths.** The `scripts/…` paths below are relative
+> to **this skill's own directory** (where this `SKILL.md` lives) — NOT the
+> project being migrated. When running inside a target repo, invoke them by
+> absolute path, e.g.
 > `python3 "$SKILL_DIR/scripts/extract_cmake.py" …` where `$SKILL_DIR` is this
 > skill's install location (e.g. `~/.claude/skills/any2bazel`). The artifacts
 > you *produce* — `model.*.json`, `aquery.json`, `diff.json`, the generated
@@ -399,16 +399,8 @@ build brings (no action graph to extract, traversal-order-dependent output,
 `node_modules` as both toolchain and foreign Bazel package):
 [docs/CASE-vscode-migration.md](docs/CASE-vscode-migration.md).
 
-## Tests
+## Updating this skill
 
-```bash
-python3 tests/test_engine.py && python3 tests/test_extractors.py \
-    && python3 tests/test_maven.py && python3 tests/test_extract_npm.py \
-    && python3 tests/test_triage.py && python3 tests/test_configure.py
-```
-
-Extractor tests run against fixtures that mirror the documented File API,
-aquery, Maven argfile, and npm-NDJSON schemas. When a real project surfaces a
-schema detail the extractors mishandle (fragment quoting, `external/` repo paths
-in aquery, multi-config), fix the extractor and capture that output as a new
-fixture.
+To change this skill or its scripts, read
+[CONTRIBUTING.md](CONTRIBUTING.md) first. It covers testing and presubmit
+requirements.